1. Field of the Invention
The present invention relates to a recording medium.
2. Description of the Related Art
In recent years, researches and developments have been made to various recording materials, such as inkjet recording mediums and thermosensitive recording mediums, in the field of information recording, and the results thereform have also be made into practice so as to meet the diversity of information and needs in the art.
An inkjet recording system is a system where images or characters are recorded by jetting small droplets of an ink according to various operating principles, and depositing the ink on a recording medium such as a piece of paper.
Printers applying the inkjet recording system have characteristics such that a recording can be performed at high speed and with low noise, images can be easily produced in various colors, there is a large flexibility in recording patterns, and no special developing and/or fixing processing is necessary. For these reasons, use of such printers has been rapidly spread as recording devices of various images in various applications including information devices.
Moreover, the inkjet recording system has recently been significantly improved as the technology that enables to attain images of high accuracy and high quality.
Furthermore, the inkjet recording system has been rapidly developed to occupy a large part of the market of the image forming technology, resulted from the rapid spread of personal computers or internet, or the social needs such as the necessity of visual presentations.
However, along with the improvements of performances, e.g. a recording speed, of the recent inkjet printers, some of the inkjet printers generates a large amount of static electricity.
Especially, the static electricity generated near a surface of an ink-receiving layer is problematic, and this gives adverse influence to handlings such as conveyance, also scattering an ink at the time of recording to thereby cause background depositions.
Since particles contained in an ink have recently been getting smaller and smaller to achieve high accuracy and high image quality, such particles are easily influenced by static electricity. Therefore, occurrences of background depositions become a serious problem.
Moreover, static electricity also causes, other than background depositions, inferior conveyance such as conveyance of sheets with being stacked, at the time when recording mediums in the shape of sheets are conveyed, causing paper jam in the conveyance system. Therefore, an improvement is desired to solve such the problems.
To solve such problems due to static electricity, an antistatic agent is added to an inkjet recording medium.
For example, Japanese Patent Application Laid-Open (JP-A) No. 2004-196988 discloses that an inkjet recording medium the size or shape of which can be easily changed by using a conductive conjugated polymer in the ink recording medium.
Moreover, JP-A Nos. 2001-11125 and 2005-511343 disclose that an inkjet recording medium of excellent antistatic property can be provided by using an ionic antistatic agent as an antistatic agent.
However, the antistatic agent using such ionic conductivity exhibits its antistatic function due to absorbing absorption thereof, and thus has poor water resistance. Therefore, in the case where a recording medium is immersed in water after inkjet recording, the recorded image is smeared, or is in the wet condition so that the image bleeding is caused with rubbing, to thereby lower the image density.
Moreover, the antistatic effect thereof tends to depend on the humidity, and such antistatic agent has weak antistatic function under the low temperature-low humidity environment.
Furthermore, JP-A No. 2005-231095 discloses an inkjet recording medium including an ink-receiving layer, in which the ink-receiving layer is formed of a high molecular binder material and is doped with metal antimonate such as zinc antimonate, and JP-A No. 2003-182206 discloses an inkjet recording medium having an ink-receiving layer containing a conductive polymer and metal antimonate such as zinc antimonate.
The antimony compound has a high antistatic effect compared to other inorganic antistatic agents, and thus is a material which has been used for a long time. However, the antimony compound is Class 1 Designated Chemical Substance, meaning that the antimony compound is harmful and thus designated by the government as a substance a handling of which needs to be controlled and monitored. Therefore, use of such compound in a product that can be touched by people, such as an inkjet recording medium, is not preferable in view of hazard thereof.
Furthermore, JP-A No. 2002-356057 discloses an ink-receiving body having a back layer using conductive tin oxide sol particles as an antistatic agent. However, such the conductive tin oxide sol particles are extremely expensive, and thus it is a current situation that such expensive material cannot be used for a recording medium which is sold at low price, such as an inkjet recording medium. JP-A No. 2000-250250 discloses a recording paper which is formed by making paper from pulp slurry containing at least two white extender pigments selected from titanium dioxide, calcium carbonate, and white carbon, and size pressing using a surface sizing agent containing an antistatic agent and a high molecular binder material. This recording paper is excellent as it has an anti-offset effect and prevents bleeding.
Accordingly, an inkjet recording medium which has high ink absorption, excellent water resistance, excellent antistatic properties, excellent properties for preventing the powder from falling off and high safety has been strongly desired to be provided.
Thermosensitive recording mediums have advantages such as (1) images are easily recorded only by a heating process; and (2) a device for use has a simple mechanism and can be easily downsized and the recording medium is easy to handle and cheap.
Therefore, the techniques of the thermosensitive recording have been used in various fields, such as information processing (e.g. output such as electronic desk calculators, and computers), recorders for medical instrumentations, low and high speed facsimiles, automated ticket vendors (for thickets such as railway tickets, and admission tickets), thermosensitive copying, labeling of POS system, and tabs.
In the thermosensitive recording medium, a coloring substance-containing layer is generally disposed on a paper support, and the coloring substance induces a coloring reaction by heating. The thermosensitive recording medium used for thickets is mounted to a printer in the shape of a roll, and is cut by a cutter disposed at the printer outlet after the image formation by a thermal head, to thereby give out a thicket.
However, paper powder is generated from the support when cut at the printer outlet, and is accumulated inside the printer as a number of given thickets is increased.
According to this, the paper powder and also dusts scattered in the air are deposited onto a surface of a thermosensitive recording medium by static electricity generated by a friction with a platen roll or a thermal head during printing in the printer, the deposited paper powder or dusts are nipped between the thermosensitive recording medium and the thermal head during printing, so that an image failure such as a phenomenon that a blank portion is formed in the shape of lines within the image at or near the part where the paper powder or dusts are deposited (hereinafter this phenomenon is referred as white lines), tends to be occurred.
To solve these problems, there is proposed a thermosensitive recording medium in which an antistatic agent is added in a recording surface or the opposite surface (hereinafter, may be referred as a back layer).
For this antistatic agent, (1) inorganic salts such as sodium chloride, (2) anionic polymer electrolytes such as sodium polystyrene sulfonate, and (3) conductive oxides such as conductive zinc oxide and conductive tin oxide, or conductive metal compounds such as silver, copper, nickel are used.
For example, JP-A No. 2007-76251 discloses a thermosensitive recording medium including a back layer using a binder resin material containing an antistatic agent formed of polyalkylene glycol and lithium perchlorate, and JP-A No. 2007-223257 discloses a thermosensitive recording material including a back layer using a crosslinkable acrylic emulsion binder material containing a water-soluble organic polymer antistatic agent.
However, the inorganic salts such as sodium chloride and the anionic polymer electrolytes such as sodium polystyrene sulfonate has a low effect considering the amount thereof to be added, and change their antistatic performances depending on the humidity. Moreover, they have stickiness under the high humidity environment because of the properties of the electrolytes thereof, and are hard to be dissolved in water.
JP-A No. 63-230388 discloses a thermosensitive recording material including a back layer using a binder resin material containing an antistatic agent that is conductive oxide titanium powder, the conductive oxide titanium powder being prepared by processing tin oxide powder with antimony oxide. JP-A No. 63-230388 also discloses that this conductive titanium oxide antistatic agent is “produced by a method containing adding a hydrochloric solution of antimony chloride and tin chloride into a suspension of titanium oxide powder, and hydrolyzing antimony chloride and tin chloride on the surface of each titanium oxide powder,” but such description is far from the conventional method in which a hydrolyzing metal compound in the solution is hydrolyzed in the presence of alkali to form hydroxide, and hydroxide is sintered so as to modify the same into oxide. Other than that, the conductive metal compound exhibit an effect with a small amount thereof without depending on the temperature, but it has a drawback in terms of safety.
Moreover, the thermosensitive recording medium is used as a POS label for food or a thicket. Accordingly, the material may be wet with water in case of the label for fresh food, and may be wet with rain outside in case of the ticket, and thus it is important that the thermosensitive recording material has a water-proof property for the use of the thermosensitive recording medium.
Accordingly, it is a current situation that there has been strongly desired a thermosensitive recording medium, which has a low charging amount during printing, a low amount of the paper powder generated at the time of cutting the medium to thereby reduce conveyance failures or a deposition amount of the powder or dusts on the printing surface, is highly sensitive and excellent in storage stability, is excellent in terms of safety without influencing the environment, and has excellent water resistance.